The bicycle of folding type have become more and more popular nowadays. But several disadvantages still exist therein. Some of them have too complicated folding mechanism causing a high cost as well as a high price, and lose the popularity in marketing. Some other have poor structure and were subject to the possibility of coming apart unexpectedly due to wear and tear of their engaging portions and operation of the folding mechanism wherein the folding of bicycle often can not be easily done, and the safety of use can not be insured.
Therefore, the primary object of the present invention is to provide a folding bicycle with improved hinge mechanism for frame assembly which make it possible to unfold the frame assemblies and put the bicycle into a riding position easily and quickly.
Another object of the present invention is to provide a folding bicycle which is adapted to it frame structure fixed with absolute rigidity and safety when they are secured in the riding position.
A further object of the present invention is to provide a folding bicycle which can be folded in type of that two handle bars are ridden astride both the front wheel and the rear wheel when two handle bar structure are folding downwordly and the main pedal sprocket and the sprocket chain are protected by the front and the rear wheels so as to achieve a compact and portable structure.